1) What are the
Back ground processes in Oracle and what are they.
This is one of the most frequently asked
question.There are basically 9 Processes but in a
general
system we need to mention the first five background processes.They do the house
keeping
activities
for the Oracle and are common in any system.
The
various background processes in oracle are
a)
Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks from
Database buffer cache to Data Files.This is required since the data is not
written whenever a transaction is commited.
b)LogWriter(LGWR) ::
LogWriter writes the redo log entries to disk. Redo Log data is
generated in redo log buffer of SGA. As transaction commits and log buffer
fills, LGWR writes log entries into a online redo log file.
c)
System Monitor(SMON) :: The System Monitor performs instance recovery at
instance startup.This is useful for recovery from system failure
d)Process
Monitor(PMON) :: The Process Monitor peforms process recovery when user Process
fails. Pmon Clears and Frees resources that process was using.
e) CheckPoint(CKPT) :: At Specified times, all
modified database buffers in SGA are written to data files by DBWR at Checkpoints
and Updating all data files and control files of database to indicate the
most
recent checkpoint
f)Archieves(ARCH)
:: The Archiver copies online redo log files to archival storal when they are
busy.
g)
Recoveror(RECO) :: The Recoveror is used to resolve the distributed transaction in network
h)
Dispatcher (Dnnn) :: The Dispatcher is useful in Multi Threaded Architecture
i)
Lckn :: We can have upto 10 lock processes for inter instance locking in
parallel sql.
2) How many
types of Sql Statements are there in Oracle
There are basically 6 types of sql
statments.They are
a)
Data Defination Language(DDL) :: The DDL
statments define and maintain objects and drop objects.
b)
Data Manipulation Language(DML) :: The DML statments manipulate database data.
c)
Transaction Control Statements ::
Manage change by DML
d)
Session Control :: Used to
control the properties of current session enabling and disabling roles and
changing .e.g :: Alter Statements,Set
Role
e)
System Control Statements
:: Change Properties of Oracle Instance .e.g:: Alter System
f)
Embedded Sql ::
Incorporate DDL,DML and T.C.S in Programming Language.e.g:: Using the Sql
Statements in languages such as 'C', Open,Fetch, execute and close
3) What is a
Transaction in Oracle
A transaction is a Logical unit of work that compromises one or
more SQL Statements executed by a single User. According to ANSI, a transaction
begins with first executable statment and ends when it is explicitly commited
or rolled back.
4) Key Words Used in Oracle
The Key words that are used in Oracle are ::
a) Commiting :: A transaction is said to be
commited when the transaction makes permanent
changes resulting from the SQL statements.
b) Rollback :: A transaction that retracts any of the
changes resulting from SQL statements in Transaction.
c)
SavePoint :: For long
transactions that contain many SQL statements, intermediate markers or
savepoints are declared. Savepoints can be used to divide a transactino into
smaller points.
d) Rolling Forward :: Process of applying redo log during recovery is called rolling
forward.
e) Cursor :: A cursor is a handle ( name
or a pointer) for the memory associated with a specific stament. A cursor is basically an area allocated by
Oracle for executing the Sql Statement. Oracle uses an implicit cursor
statement for Single row query and Uses Explcit cursor for a multi row query.
f)
System Global Area(SGA) :: The SGA is a shared memory region allocated by the
Oracle that contains Data and control information for one Oracle Instance.It
consists of Database Buffer Cache and Redo log Buffer.
g)
Program Global Area (PGA) :: The PGA is a memory buffer that contains data and control information
for server process.
g)
Database Buffer Cache :: Databese Buffer of SGA stores the most recently used
blocks of datatbase data.The set of database buffers in an instance is called
Database Buffer Cache.
h)
Redo log Buffer :: Redo log Buffer of
SGA stores all the redo log entries.
i)
Redo Log Files :: Redo log files are
set of files that protect altered database data in memory that has not been
written to Data Files. They are basically used for backup when a database
crashes.
j)
Process :: A Process is
a 'thread of control' or mechansim in Operating System that executes series of
steps.
5) What are
Procedure,functions and Packages
Procedures
and functions consist of set of PL/SQL statements that are grouped
together as a unit to solve a specific problem or perform set of related tasks.
Procedures do not Return values while
Functions return one One Value
Packages :: Packages Provide a method of
encapsulating and storing related procedures, functions, variables and other
Package Contents
6) What are
Database Triggers and Stored Procedures
Database Triggers :: Database Triggers are
Procedures that are automatically executed as a result of insert in, update to,
or delete from table.
Database triggers have the values old and new
to denote the old value in the table before it is deleted and the new indicated
the new value that will be used. DT are useful for implementing complex
business rules which cannot be enforced using the integrity rules.We can have
the trigger as Before trigger or After Trigger and at Statement or Row level.
e.g::
operations insert,update ,delete 3
before ,after 3*2 A total of 6 combinatons
At statment level(once for the trigger)
or row level( for every execution )
6 * 2 A total of 12.
Thus a total of 12 combinations are there and
the restriction of usage of 12 triggers has been lifted from Oracle 7.3
Onwards.
Stored
Procedures :: Stored Procedures are
Procedures that are stored in Compiled form in the database.The advantage of
using the stored procedures is that many users can use the same procedure in
compiled and ready to use format.
7) How many
Integrity Rules are there and what are they
There are Three Integrity Rules. They are as
follows ::
a)
Entity Integrity Rule :: The Entity Integrity Rule enforces that the Primary key cannot be Null
b)
Foreign Key Integrity Rule :: The FKIR denotes that the relationship between
the foreign key and the primary key has to be enforced.When there is data in
Child Tables the Master tables cannot be deleted.
c)
Business Integrity Rules :: The Third Intigrity rule is about the complex
business processes which cannot be implemented by the above 2 rules.
8) What are the
Various Master and Detail Relation ships.
The various Master and Detail Relationship are
a)
NonIsolated :: The Master cannot be deleted when a child is exisiting
b)
Isolated :: The Master can be
deleted when the child is exisiting
c)
Cascading :: The child gets deleted
when the Master is deleted.
9) What are the
Various Block Coordination Properties
The various Block Coordination Properties are
a)
Immediate
Default
Setting. The Detail records are shown when the Master Record are shown.
b)
Deffered with Auto Query
Oracle
Forms defer fetching the detail records until the operator navigates to the
detail block.
c)
Deffered with No Auto Query
The
operator must navigate to the detail block and explicitly execute a query
10) What are the
Different Optimisation Techniques
The Various Optimisation techniques are
a)
Execute Plan :: we can see the plan of the query and change it accordingly
based on the indexes
b)
Optimizer_hint ::
set_item_property('DeptBlock',OPTIMIZER_HINT,'FIRST_ROWS');
Select
/*+ First_Rows */ Deptno,Dname,Loc,Rowid from dept
where
(Deptno > 25)
c)
Optimize_Sql ::
By
setting the Optimize_Sql = No, Oracle Forms assigns a single cursor for all SQL
statements.This slow downs the processing because for evertime the SQL must be
parsed whenver they are executed.
f45run
module = my_firstform userid = scott/tiger optimize_sql = No
d)
Optimize_Tp ::
By setting the Optimize_Tp= No, Oracle Forms
assigns seperate cursor only for each query SELECT statement. All other SQL statements reuse the
cursor.
f45run
module = my_firstform userid = scott/tiger optimize_Tp = No
11) How do u
implement the If statement in the Select
Statement
We can implement the if statement in the
select statement by using the Decode statement.
e.g
select DECODE
(EMP_CAT,'1','First','2','Second'Null);
Here
the Null is the else statement where null is done .
12)How many
types of Exceptions are there
There are 2 types of exceptions. They are
a)
System Exceptions
e.g.
When no_data_found, When too_many_rows
b)
User Defined Exceptions
e.g.
My_exception exception
When
My_exception then
13) What are the
inline and the precompiler directives
The inline and precompiler directives detect
the values directly
14) How do you
use the same lov for 2 columns
We can use the same lov for 2 columns by
passing the return values in global
values and using the global values in the code
15) How many
minimum groups are required for a matrix report
The
minimum number of groups in matrix report are 4
16) What is the
difference between static and dynamic lov
The static lov contains the predetermined
values while the dynamic lov contains
values that come at run time
17) What are
snap shots and views
Snapshots are mirror or replicas of tables.
Views are built using the columns from one or more tables. The Single Table
View can be updated but the view with multi table cannot be updated
18) What are the
OOPS concepts in Oracle.
Oracle does implement the OOPS concepts. The
best example is the Property Classes. We can categorise the properties by
setting the visual attributes and then attach the property classes for the
objects.
OOPS supports the concepts of objects and classes and we can consider the
peroperty classes as classes and the items as objects
19) What is the difference between candidate key,
unique key and primary key
Candidate keys are the columns in the table
that could be the primary keys and the primary key
is
the key that has been selected to identify the rows. Unique key is also useful
for identifying the distinct rows in the
table.
20)What is
concurrency
Cuncurrency is
allowing simultaneous access of same data by different users. Locks useful for accesing the database are
a)
Exclusive
The
exclusive lock is useful for locking the row when an insert,update or delete is
being done.This lock should not be applied
when we do only select from the row.
b)
Share lock
We
can do the table as Share_Lock as many share_locks can be put on the same
resource.
21) Previleges and
Grants
Previleges
are the right to execute a
particulare type of SQL statements.
e.g
:: Right to Connect, Right to create, Right to resource
Grants
are given to the objects so that the object might be accessed accordingly.The
grant has to be
given
by the owner of the object.
22)Table
Space,Data Files,Parameter File, Control Files
Table
Space :: The table space is useful for storing the data in the database.When a
database is created two table spaces are created.
a)
System Table space :: This data file stores all the tables related to the
system and dba tables
b)
User Table space :: This data file
stores all the user related tables
We
should have seperate table spaces for storing the tables and indexes so that
the access is fast.
Data
Files :: Every Oracle Data Base has one or more physical data files.They store
the data for the database.Every datafile is associated with only one
database.Once the Data file is created the size cannot change.To increase the
size of the database to store more data we have to add data file.
Parameter
Files :: Parameter file is needed to start an instance.A parameter file
contains the list of instance configuration parameters e.g.::
db_block_buffers
= 500
db_name
= ORA7
db_domain
= u.s.acme lang
Control
Files :: Control files record the
physical structure of the data files and redo log files
They
contain the Db name, name and location of dbs, data files ,redo log files and
time stamp.
23) Physical
Storage of the Data
The
finest level of granularity of the data base are the data blocks.
Data
Block :: One Data Block correspond to
specific number of physical database space
Extent :: Extent is the number of specific
number of contigious data blocks.
Segments ::
Set of Extents allocated for Extents. There are three types of Segments
a)
Data Segment :: Non Clustered Table has data segment data of every table is stored in
cluster
data segment
b)
Index Segment :: Each Index has index segment that stores data
c)
Roll Back Segment :: Temporarily store 'undo' information
24) What are the
Pct Free and Pct Used
Pct Free is used to denote the percentage of
the free space that is to be left when creating a table. Similarly Pct Used is
used to denote the percentage of the used space that is to be used when
creating a table
eg.::
Pctfree 20, Pctused 40
25) What is Row
Chaining
The data of a row in a table may not be able
to fit the same data block.Data for row is stored in a chain of data blocks .
26) What is a 2
Phase Commit
Two Phase commit is used in distributed data
base systems. This is useful to maintain the integrity of the database so that
all the users see the same values. It contains DML statements or Remote
Procedural calls that reference a remote object. There are basically 2 phases in
a 2 phase commit.
a)
Prepare Phase :: Global coordinator asks participants to prepare
b)
Commit Phase :: Commit all participants
to coordinator to Prepared, Read only or abort Reply
27) What is the difference between deleting and truncating of tables
Deleting
a table will not remove the rows from the table but entry is there
in the database dictionary and it can be
retrieved But truncating a table deletes it completely and it cannot be
retrieved.
28) What are
mutating tables
When a table is in state of transition it is
said to be mutating. eg :: If a row has been deleted then the table is said to
be mutating and no operations can be done on the table except select.
29) What are Codd Rules
Codd Rules describe the ideal nature of a
RDBMS. No RDBMS satisfies all the 12 codd rules and Oracle Satisfies 11 of the
12 rules and is the only Rdbms to satisfy the maximum number of rules.
30) What is
Normalisation
Normalisation is the process of organising the
tables to remove the redundancy.There are mainly 5 Normalisation rules.
a)
1 Normal Form :: A table is said to be
in 1st Normal Form when the attributes are atomic
b)
2 Normal Form :: A table is said to be
in 2nd Normal Form when all the candidate keys are dependant on the primary key
c)
3rd Normal Form :: A table is said to be third Normal form when it is not
dependant transitively
31) What is the
Difference between a post query and a pre query
A post query will fire for every row that is
fetched but the pre query will fire only once.
32) Deleting the
Duplicate rows in the table
We can delete the duplicate rows in the table
by using the Rowid
33)
Can U disable database trigger? How?
Yes. With respect to table
ALTER TABLE TABLE
[ DISABLE all_trigger ]
34)
What is pseudo columns ? Name them?
A
pseudocolumn behaves like a table column, but is not actually
stored in the table. You can
select from pseudocolumns, but you
cannot insert, update, or delete their values. This section
describes these pseudocolumns:
* CURRVAL
* NEXTVAL
* LEVEL
* ROWID
* ROWNUM
35)
How many columns can table have?
The number of columns in a table
can range from 1 to 254.
36)
Is space acquired in blocks or extents ?
In extents .
37)
what is clustered index?
In an indexed cluster, rows are stored
together based on their cluster key values .
Can not applied for HASH.
38)
what are the datatypes supported By oracle (INTERNAL)?
Varchar2, Number,Char , MLSLABEL.
39
) What are attributes of cursor?
%FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT
40)
Can you use select in FROM clause of SQL select ?
Yes.
EmoticonEmoticon